(a) Field of the Invention
The present invention relates to a positive active material for a rechargeable lithium battery, a rechargeable lithium battery including the same, and a method for manufacturing a rechargeable lithium battery. More particularly, the present invention relates to, a rechargeable lithium battery having a high-capacity, and an excellent cycle characteristic.
(b) Description of the Related Art
Rechargeable lithium batteries have been widely used as a power source for electronic devices such as a cellular phone, a digital still camera, a digital video camera, and a laptop computer. The conventional rechargeable lithium battery includes a positive active material of LiCoO2, a negative active material of graphite, and an electrolyte of a non-aqueous solution. Recently, the rechargeable lithium battery having a high capacity is required to provide power to the electronic devices. In order to satisfy the requirements, researches for the negative active materials having a main component of Si have been progressed. As the negative active material including Si as a main component has a 10 times charge and discharge capacity compared with that of the graphite, it is promising for the future candidate for the electrode material. However, the negative active material including Si forms an alloy with lithium at charging and undergoes volume expansion or electrolyte decomposition.
In order to solve the problem, the negative active material including a multi-phase alloy powder in which is composed of the main-component of Si but Si is removed on the surface has been developed (Japanese Patent laid-open No. 2005-071772). Thereby, the utilization of the negative active material including Si is almost realized. When Li is deintercalated from the positive active material due to the charge the conventional rechargeable lithium battery, the positive active material is become to electrochemically unstable and the metal thereof such as Co is eluted to be deteriorated. Thereby, the cycle characteristic and the safety are deteriorated upon charging the battery since the positive active material is deteriorated. Further, since the deterioration of the positive active material is more remarkable if it is higher capacity, it is hard to obtain a rechargeable lithium battery having both a high capacity and excellent cycle characteristic and safety.